Detector unit for mammography, and a nuclear medicine diagnostic apparatus for mammography having the same

ABSTRACT

A detector unit for mammography of this invention includes a gamma-ray detector having a configuration with a cutout formed in part of a closed curve, a hollow portion thereof providing a field of view. The gamma-ray detector can easily be placed in a position where a breast and breast peripheries of a patient enter the field of view at the same time, by fitting sites of the patient not to be examined, such as a top of an arm and a shoulder, in the cutout. This allows breast tissues present in the breast and breast peripheries to be diagnosed at the same time.

TECHNICAL FIELD

This invention relates to a detector unit for mammography having agamma-ray detector for detecting gamma rays released from a patient, anda nuclear medicine diagnostic apparatus for mammography having the same.

BACKGROUND ART

Conventionally, an ordinary nuclear medicine diagnostic apparatusincludes a gamma-ray detector in a circular or polygonal ring form fordetecting gamma rays, and an image processor for producing an RIdistribution image based on emission data obtained from the gamma-raydetector. The gamma-ray detector includes a scintillator with numerousscintillator chips for emitting light upon incidence of gamma rays, anda photomultiplier tube for converting the light emissions of thescintillator into electric signals.

A patient is placed in the hollow portion of the gamma-ray detector, andthe patient is injected with a radioactive drug labeled with apositron-emitting radioisotope. The positron-emitting radioisotopedistributed in the body releases two gamma rays in 180-degree oppositedirections. The gamma-ray detector detects the gamma rays released fromthe patient. Then, the image processor collects, as emission data,events of a pair of gamma rays counted as coincidence, and produces atwo-dimensional or three-dimensional RI distribution image based on thisemission data. The RI distribution image produced is suitable mainly fordiagnosing presence or absence, position, malignancy and so on of atumor.

Conventionally, there is also a nuclear medicine diagnostic apparatusused mainly for radiographing the breasts (hereinafter called thenuclear medicine diagnostic apparatus for mammography). In the case ofbreast cancer also, it is effective to find a smaller tumor for the sakeof early detection. Therefore, the size of the scintillator chips isreduced, and the gamma-ray detector is constructed to be set close tothe patient (see Patent Document 1, for example).

[Patent Document 1]

-   Japanese Unexamined Patent Publication No. 2003-325499

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

However, the conventional example with such construction has thefollowing drawback.

The conventional nuclear medicine diagnostic apparatus for mammographycan place the gamma-ray detector around a breast, but the range of anarmpit, a shoulder joint and so on (hereinafter called simply the breastperipheries) cannot be put into the field of view because of thegamma-ray detector hitting against the arm or shoulder. However, breasttissues exist in the breast peripheries as well as the breast, and abreast cancer can develop there. While the breast peripheries also aresites to be examined along with the breast, the conventional example hasan inconvenience that the breast tissues of the breast peripheriescannot be diagnosed at the time of diagnosis of the breast.

This will be described with reference to FIG. 11. FIG. 11 is a viewshowing a positional relationship between the gamma-ray detector andpatient M according to the conventional example. The gamma-ray detector61 in the shape of a ring can be placed to surround a breast m1, and thebreast m1 comes into its field of view. However, since breastperipheries m2 cannot be put into the field of view, as shown, thebreast tissues of the breast peripheries cannot be diagnosed.

This invention has been made having regard to the state of the art notedabove, and its object is to provide a detector unit for mammography anda nuclear medicine diagnostic apparatus for mammography having the same,which are capable of putting a breast and peripheries of the breast(armpit, shoulder joint and so on) into a field of view.

Means for Solving the Problem

To fulfill the above object, this invention provides the followingconstruction.

This invention is a detector unit for mammography comprising a gamma-raydetector having a configuration with a cutout formed in part of a closedcurve or a polygon having a hollow portion, the hollow portion providinga field of view.

According to the detector unit for mammography of this invention, in acase that, when placing the gamma-ray detector on a breast, thegamma-ray detector cannot closely contact the breast because sites notto be examined are obstructive, the sites not to be examined may befitted in the cutout, thereby allowing the gamma-ray detector to contactthe breast closely. Since the sites not to be examined are notobstructive, the gamma-ray detector can easily be placed in a positionwhere the breast and breast peripheries enter the field of view at thesame time. As a result, breast tissues present in the breast and breastperipheries can be diagnosed efficiently.

The invention set out in claim 2 is a detector unit for mammographycomprising a gamma-ray detector having a configuration with a cutoutformed in part of a ring shape having a hollow portion, the hollowportion providing a field of view.

According to the detector unit for mammography of this invention, in acase that, when placing the gamma-ray detector on a breast, thegamma-ray detector cannot closely contact the breast because sites notto be examined are obstructive, the sites not to be examined may befitted in the cutout, thereby allowing the gamma-ray detector to contactthe breast closely. Since the sites not to be examined are notobstructive, the gamma-ray detector can easily be placed in a positionwhere the breast and breast peripheries enter the field of view at thesame time. As a result, breast tissues present in the breast and breastperipheries can be diagnosed efficiently.

In this invention, it is preferred that the hollow portion is capable ofreceiving a breast (claim 3). The breast can be placed in the field ofview conveniently.

In this invention, it is preferred that the gamma-ray detector can bepositioned so that, when a top of an arm or a shoulder is inserted inthe cutout, at least one of an armpit and a shoulder joint, and thebreast, enter the field of view of the gamma-ray detector (claim 4). Thebreast and breast peripheries can be placed in the field of view of thegamma-ray detector at the same time. Thus, breast tissues present in thebreast and breast peripheries can be diagnosed at the same time.

The invention set out in claim 5 is a detector unit for mammographycomprising a gamma-ray detector shaped to surround a lower part of abreast, with one end region thereof placeable up to a shoulder jointabove the breast, and the other end region placeable up to an armpitpresent laterally of the breast, wherein the gamma-ray detector has afield of view corresponding to a hollow portion formed inwardly thereof.

According to the detector unit for mammography of this invention, whenplacing the gamma-ray detector on a breast, the gamma-ray detector canclosely contact the breast in the absence of obstructions presented byan arm and a shoulder. The breast and an armpit or/and a shoulder jointcan be placed in the field of view of the gamma-ray detector. Thus,breast tissues present in the breast and breast peripheries can bediagnosed efficiently.

The invention set out in claim 6 is a detector unit for mammographycomprising a gamma-ray detector shaped to extend downward from an armpitto a lower part of a breast, turn back along the lower part of thebreast, and extend to a shoulder joint above the breast, wherein thegamma-ray detector has a field of view corresponding to a hollow portionformed inwardly thereof.

According to the detector unit for mammography of this invention, whenplacing the gamma-ray detector on a breast, the gamma-ray detector canclosely contact the breast in the absence of obstructions presented byan arm and a shoulder. The breast and an armpit or/and a shoulder jointcan be placed in the field of view of the gamma-ray detector. Thus,breast tissues present in the breast and breast peripheries can bediagnosed efficiently.

In this invention, it is preferred that the gamma-ray detector isplaceable along a body surface of the patient (claim 7). The gamma-raydetector can be placed in closer contact with a breast and other sites.

In this invention, it is preferred that the gamma-ray detector has ahorseshoe shape or a shape of letter U (claim 8).

In this invention, it is preferred that the hollow portion issubstantially circular (claim 9). The substantially circular shapeincludes a perfect circle, a circle close to a perfect circle, and apolygon approximating to a perfect circle, and also includes a shapepartly deformed with a cutout or the like.

In this invention, it is preferred that the hollow portion is 160 mm to250 mm in diameter (claim 10). A breast and the like can be diagnosedconveniently.

In this invention, it is preferred that the cutout is 50 to 150 mm inlength (claim 11). A breast and the like can be diagnosed conveniently.

In this invention, it is preferred that the hollow portion isapproximately teardrop-shaped or approximately elliptical (claim 12).The breast peripheries can be put into the field of view more properly.The approximately teardrop shape or approximately elliptical shapeincludes a case of a part being cut off by a cutout or the like.

In this invention, it is preferred that the gamma-ray detector has alarger curvature radius in end regions thereof than in regions otherthan the end regions of the gamma-ray detector (claim 13). The breastperipheries can be put into the field of view more properly.

In this invention, it is preferred that the hollow portion is columnar(claim 14).

In this invention, it is preferred that the gamma-ray detector hasdetecting planes vertical to a bottom plane of the hollow portion (claim15).

In this invention, it is preferred that the gamma-ray detector hasdetecting planes inclined relative to a bottom plane of the hollowportion (claim 16).

In this invention, it is preferred that the gamma-ray detector isdisplaced axially of the hollow portion (claim 17). With the gamma-raydetector twisted axially of the hollow portion, the breast peripheriescan be put into the field of view properly.

In this invention, it is preferred that the gamma-ray detector isdivided into two split detectors; wherein the split detectors have oneends thereof separated from each other, and the other ends joinedtogether to render detecting planes of the split detectors continuous;the unit further comprising a split pivotal holding device for pivotablyholding at least one of the split detectors, whereby the hollow portioncan be enlarged and reduced in size (claim 18). The hollow portion canbe enlarged or reduced in size according to the size and shape of abreast.

In this invention, it is preferred that a plate-like object is providedfor closing an outside of a field of view at one side of the hollowportion (claim 19). The breast will never protrude from the field ofview.

In this invention, it is preferred that an armrest member in form of aflat plate or a curved plate is provided for closing the cutout (claim20). The armrest member provided can prevent an excessive entry of sitesnot to be examined such an arm and a shoulder, thereby allowing breasttissues to be diagnosed conveniently.

In this invention, it is preferred that a restricting member is disposedin the end regions of the gamma-ray detector for contacting at least oneof the top of the arm and the shoulder to restrict entry of the arm andthe shoulder to the hollow portion (claim 21). The restricting memberprovided can prevent entry of an arm and a shoulder, thereby allowingbreast tissues to be diagnosed conveniently.

The invention set out in claim 22 is a detector unit for mammographycomprising a gamma-ray detector having a configuration with a cutoutformed in a dome shape or conical shape having a cavity, the cavityproviding a field of view.

According to the detector unit for mammography of this invention, in acase that, when placing the gamma-ray detector on a breast, thegamma-ray detector cannot closely contact the breast because sites notto be examined are obstructive, the sites not to be examined may befitted in the cutout, thereby allowing the gamma-ray detector to coverthe entire breast. Since the sites not to be examined are notobstructive, the gamma-ray detector can easily be placed in a positionwhere the breast and breast peripheries enter the field of view at thesame time. As a result, breast tissues present in the entire breast andbreast peripheries can be diagnosed efficiently.

In this invention, it is preferred that the cavity is capable ofreceiving a breast (claim 23). The breast can be placed in the field ofview conveniently.

In this invention, it is preferred that, when a top of an arm or ashoulder is inserted in the cutout, at least one of an armpit and ashoulder joint, and the breast, can be positioned to enter the field ofview of the gamma-ray detector (claim 24). The breast and breastperipheries can be placed in the field of view of the gamma-ray detectorat the same time. Thus, breast tissues present in the breast and breastperipheries can be diagnosed at the same time.

In this invention, it is preferred that a rotary support device isprovided for rotatably supporting the gamma-ray detector (claim 25).Diagnoses of the right and left breasts can be switched easily.

In this invention, it is preferred that the rotary support devicesupports the gamma-ray detector to be rotatable about an axis of thehollow portion (claim 26).

The invention set out in claim 27 is a nuclear medicine diagnosticapparatus for mammography comprising a detector unit for mammographyaccording to any one of claims 1 to 26; and an image processing devicefor obtaining an RI distribution image based on emission data collectedfrom the detector unit for mammography.

According to the nuclear medicine diagnostic apparatus for mammographyof this invention, an RI distribution image of breast tissues present ina breast and breast peripheries can be produced. Thus, the breasttissues present in the breast and breast peripheries can be diagnosedefficiently.

Effects of the Invention

According to the detector unit for mammography of this invention, in acase that, when placing the gamma-ray detector on a breast, thegamma-ray detector cannot closely contact the breast because sites notto be examined are obstructive, the sites not to be examined may befitted in the cutout, thereby allowing the gamma-ray detector to contactthe breast closely. Since the sites not to be examined are notobstructive, the gamma-ray detector can easily be placed in a positionwhere the breast and breast peripheries enter the field of view at thesame time. As a result, breast tissues present in the breast and breastperipheries can be diagnosed efficiently.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an outline of a nuclear medicinediagnostic apparatus for mammography according to an embodiment;

FIG. 2 (a) is a view in horizontal section of a detector;

FIG. 2 (b) is a view in vertical section taken on line a-a of FIG. 2(a);

FIG. 3 is a perspective view of a detector block;

FIG. 4 is a view schematically showing a positional relationship betweenthe detector and a patient;

FIG. 5 (a) is a view in horizontal section of a detector according to amodified embodiment;

FIG. 5 (b) is a view in vertical section taken on line b-b of FIG. 5(a);

FIG. 6 is a view schematically showing a positional relationship betweenthe detector and a patient according to the modified embodiment;

FIG. 7 is a view in horizontal section of a detector according to amodified embodiment;

FIG. 8 (a) is a plan view of a detector according to a modifiedembodiment;

FIG. 8 (b) is a view in vertical section thereof;

FIG. 9 is a view in horizontal section of a detector according to amodified embodiment;

FIG. 10 is a perspective view of a detector according to a modifiedembodiment; and

FIG. 11 is a view schematically showing a positional relationshipbetween a detector and a patient according to a conventional example.

DESCRIPTION OF REFERENCES

-   -   1 . . . detector unit for mammography    -   3 . . . image processor    -   11, 12, 13, 14, 15, 16 . . . detectors (gamma-ray detectors)    -   17 . . . rotary support    -   18 . . . armrest member    -   19 . . . plate-like member    -   21 . . . detector blocks    -   51 . . . split pivotal holder    -   A hollow portion    -   B . . . cutout    -   C . . . detecting planes    -   P, Q . . . axis    -   M . . . patient

BEST MODE FOR CARRYING OUT THE INVENTION

The object of putting a breast and peripheries of the breast (armpit,shoulder joint and so on) into a field of view has been fulfilled by adetector unit for mammography comprising a gamma-ray detector having aconfiguration with a cutout formed in part of a closed curve or apolygon having a hollow portion, the hollow portion providing the fieldof view.

Embodiment

An embodiment of this invention will be described hereinafter withreference to the drawings. FIG. 1 is a block diagram showing an outlineof a nuclear medicine diagnostic apparatus for mammography according tothe embodiment. FIG. 2 (a) is a view in horizontal section of adetector. FIG. 2 (b) is a view in vertical section of the detector. FIG.3 is a perspective view of a detector block.

The nuclear medicine diagnostic apparatus for mammography according tothis embodiment is an apparatus for diagnosing breast tissues of apatient (human body) M, and includes a detector unit for mammography(hereinafter called simply the detector unit) 1, an image processor 3and a monitor 5.

The detector unit 1 includes a detector 11 for detecting gamma rays, arotary support 17 for rotatably supporting the detector 11, and anarmrest member 18 for receiving an arm or the like of the patient M. Thedetector 11 has a configuration having a single cutout B formed in partof a closed curve having a hollow portion A in which a breast can beplaced. In other words, the detector 11 is ring-shaped with a partthereof lacking. This detector 11 has detecting planes C formed insidethe detector 11, with the hollow portion A providing a field of view.The detector 11 corresponds to the gamma-ray detector in this invention.

A specific configuration of the detector 11 in this embodiment will bedescribed. The closed curve noted above is circular, and the detector 11is formed along the curve with part of its circumference cut out. Thehollow portion A has a diameter whose value is, for example, within arange of 160 mm to 250 mm. The cutout B has an arc length of 50 mm to150 mm, for example. However, these dimensions are not limited to theseranges.

More particularly, the detector 11 includes numerous detector blocks 21arranged along the shape of the detector 11, and a housing 23 foraccommodating these detector blocks 21.

As shown in FIG. 3, each detector block 21 is constructed of ascintillator 31 for converting gamma rays into light, a photomultiplier33 for converting the light into electric signals, and a light guide 35for leading the light from the scintillator 31 to the photomultiplier39. The scintillator 31 is an aggregate of scintillator chips 32arranged in a matrix (e.g. eight rows×eight columns) which is stacked ina plurality of stages (e.g. two stages), and its upper surface acts as adetecting plane of the detector block 21.

The detecting planes C of the detector 11 noted above are formed of thedetecting planes of the detector blocks 21 arranged to face the hollowportion A. Therefore, strictly speaking, the hollow portion A has ashape of a polygon approximating a circle as shown in FIG. 2. When thedetector blocks 21 are stacked in two stages, the detector 11 becomes amultilayer ring with the scintillator chips 32 arranged in 16 layers. Inthis embodiment, as shown in FIG. 2 (b), when seen in a sectional view,the detecting planes C are planes vertical to the bottom of the hollowportion A. Therefore, the hollow portion A has a shape of anapproximately cylindrical column (strictly, a polygon).

The rotary support 17 is connected to the housing 23, whereby thedetector 11 is rotatable about one arbitrary axis P. In this embodiment,the one axis P coincides with the central axis of the approximatelycircular hollow portion A.

The armrest member 18 is a plate-like object curved to protrude to thehollow portion A. The armrest member 18 has opposite ends thereofconnected to opposite end regions of the detector 11 opposed to eachother across the cutout B, thereby closing the cutout B. The armrestmember 18 corresponds to the armrest member in this invention, andcorresponds also to the restricting member in this invention.

The detector unit 1 further includes a plate-like member 19 for closingthe outside of the field of view at one side of the hollow portion A.The plate-like member 19 corresponds to the plate-like object in thisinvention.

The image processor 3 includes a data acquisition unit 41 and an imageprocessing unit 43. The data acquisition unit 41 collects emission datafrom results of detection by the detector unit 1. The image processingunit 43 carries out a reconstruction process based on the collectedemission data, to produce a two-dimensional or three-dimensional RIdistribution image. The monitor 5 displays the RI distribution imageproduced.

The above image processor 3 is realized by a central processing unit(CPU) for reading and executing a predetermined program, and storagemedia such as a RAM (Random-Access Memory) and a fixed disk for storinga variety of information.

Next, operation of the nuclear medicine diagnostic apparatus formammography according to Embodiment 1 will be described. FIG. 4 is aview schematically showing a positional relationship between thedetector 11 and patient M.

As shown in FIG. 4, either the right or left breast of the patient M isplaced in the hollow portion A, the top of the arm or/and the shoulderon the same side as the breast of the patient M is/are inserted in thecutout B, and the arm, for example, is placed in contact with thearmrest member 18. As a result, the detector 11 surrounds a lower partof the breast, with one end region of the detector 11 located in a rangeup to the shoulder joint above the breast, and the other end region ofthe detector 11 located in a range up to the armpit present laterally ofthe breast. Therefore, the breast peripheries such as the armpit andshoulder joint, and the breast, are placed between the detecting planesC of the detector 11 to enter the field of view of the detector 11.Because of the presence of the armrest member 18, the parts not to beexamined such as the arm and shoulder do not enter the field of view ofthe detector 11 to an excessive extent.

Next, the patient M is injected with a radioactive drug labeled with apositron-emitting radioisotope. The positron-emitting radioisotopereleases two gamma rays in 180-degree opposite directions within thepatient M. The detector 11 detects gamma rays released from the breastand the peripheries of the breast and having reached the detectingplanes C, and outputs electric signals.

The data acquisition unit 41 collects emission data from results ofdetection by the detector 11. Specifically, each electric signaloutputted from the detector 11 is once recorded in the memorysuccessively along with its position information and time information.When the detection by the detector 11 is completed, the data is readfrom the memory, events of coincidence are determined, and the eventsare counted to obtain emission data.

The image processing unit 43 carries out a reconstruction process basedon the emission data collected, to produce a two-dimensional orthree-dimensional RI distribution image. As an example of thereconstruction process, an iterative approximation image reconstruction(e.g. OSEM (Ordered Subset Expectation Maximization) algorithm (seeTakayuki Nakamura, Hiroyuki Kudo IEEE Nuclear Science SymposiumConference Record 2005 pp. 1950-54) is preferred. According to thistechnique, an RI distribution image with influences of the cutout Bsufficiently inhibited can be produced.

A simulation by the reconstruction technique in the OSEM algorithm hasbeen carried out, for example, although not shown here, by uniformlyarranging, as inscribed in a circle 208 mm in diameter, 12 detectorblocks each having scintillator chips 1.5 mm square and 4.5 mm longstacked longitudinally in four layers and arranged 32 by 32, with onedetector block omitted as the cutout B and with none omitted. It hasbeen found, as a result, that this reconstruction technique is almostentirely free from influences of the cutout B, with spatial resolutionat 70 mm from the center of the field of view being 1.3 mm for the caseof providing no cutout B, and 1.6 mm for the case of providing thecutout B.

Instead of the iterative approximation image reconstruction referred to,an existing technique may be selected, such as 3D Fourier transform,3D-FBP, rebinning, 3D reprojection or FORE (Fourier rebinning).

The RI distribution image produced is outputted to the monitor 5 asappropriate.

When the diagnosis of one of the right and left breasts is completed,the operator, for example, manually operates the rotary support 17 torotate the detector 11 about the axis P. This changes the position ofthe detector 11 to facilitate diagnosis of the other breast. Then, theother breast is diagnosed through the same procedure.

Thus, according to the nuclear medicine diagnostic apparatus formammography according to Embodiment 1, with the detector 11 which canput a breast and peripheries of the breast into the field of view at thesame time, gamma rays released from the breast and breast peripheriescan be detected. Therefore, presence or absence, position, malignancyand so on of a tumor can be suitably diagnosed for the breasts and alsofor breast tissues present around the breasts. As a result, breastcancer can be diagnosed with increased accuracy.

With the diameter of the hollow portion at 160 mm to 200 mm, and the arclength of the cutout B at 50 mm to 100 mm, a breast can be placed in thehollow portion A conveniently, and the top of the arm or the shouldercan be inserted in the cutout B.

With the detector unit 1 having the rotary support 17, the position ofthe detector 11 can be changed easily to facilitate diagnosis of each ofthe right and left breasts.

With the detector unit 1 having the plate-like member 19 for closing theoutside of the field of view at one side of the hollow portion, a breastis prevented from protruding from the field of view, and the entirebreast can be diagnosed conveniently.

The detector unit 1 with the armrest member 18 can prevent an excessiveentry of an arm, for example. Since the patient M can take a comfortableposition, the burden of the patient M can be reduced.

With the image processor 3, RI distribution images can be producedappropriately.

This invention is not limited to the foregoing embodiment, but may bemodified as follows:

(1) In the foregoing embodiment, the closed curve is a circle on thesame plane, and the detector 11 is formed along the curve with part ofits circumference cut out. This is not limitative. As long as it is aclosed curve or a polygon having a cutout in part thereof, variousshapes can be selected as appropriate. Therefore, it is not limited tobeing on the same plane, either.

Reference is made to FIGS. 5 and 6. FIG. 5 (a) is a view in horizontalsection of a detector according to a modified embodiment. FIG. 5 (b) isa view in vertical section thereof. FIG. 6 is a view schematicallyshowing a positional relationship between a detector 12 and a patient Maccording to this modified embodiment. As shown in FIGS. 5 and 6, theclosed curve is teardrop-shaped, and the detector 12 has a shapeextending along the curve with part of the tear-drop-shaped outline cutout. A cutout B is formed adjacent an upper end where theteardrop-shaped outline tapers. The field of view of the detector 12corresponds to areas of hollow portions A1 and A2. Incidentally, wherethe detector 11 described in Embodiment 1 is comparable with the widthof the detector 12, the field of view of the detector 11 can be only afield of view approximately corresponding to the hollow portion A1.Thus, with the detector 12 according to the modified embodiment, thehollow portion A2 in addition to the hollow portion A1 can provide thefield of view. A larger range of breast peripheries can be put into thefield of view (in FIG. 6, a breast and breast peripheries included inthe field of view of the detector 12 are specified by hatching).

Besides the shape of the detector 12 shown in the modified embodimentshown in FIGS. 5 and 6, a detector may be provided to have a horseshoeshape, a shape of letter U or a shape of letter C. Instead of theteardrop shape described referring to FIG. 5, a detector may be selectedto have an elliptical shape, rugby ball shape or various other outlineshapes with a cutout.

(2) Although, in the foregoing embodiment, the position of the cutout Bhas not particularly been described, but this is a matter selectable asappropriate. For example, a position in the longer direction, shorterdirection or other position of the outline of the closed curve, may beselected as appropriate. FIG. 7 refers. FIG. 7 is a view in horizontalsection of a detector according to a modified embodiment. A detector 13shown has a shape of an elliptical outline with part thereof cut out.Here, a cutout B is formed in a portion where the minor axis of theellipse intersects the elliptical outline.

(3) The shape of the detector 11 may be varied such that the curvatureradius in the opposite end regions of the detector 11 opposed to eachother across the cutout B is larger than in regions other than theopposite end regions of the detector 11. Or, where the opposite endregions of the detector 11 are not curved, a modification may be madesuch that the detecting planes C in the opposite end regions opposed toeach other across the cutout B are parallel to each other or in a nearparallel relationship. Then, the breast peripheries can be put properlyand extensively into the field of view. Specifically, the modifiedembodiment described in FIGS. 5 and 6 can be given as an example. Thatis, the detector 12 shown in FIG. 5 has a curvature radius in theopposite end regions of the detector 12 opposed to each other across thecutout B which is larger than in regions other than the opposite endregions of the detector 12.

(4) In the embodiment described hereinbefore, the hollow portion A iscolumnar, but this is not limitative. For example, a modification may bemade to incline the detecting planes C of the detector 11 relative tothe bottom of the hollow portion A. Specifically, as in the detector 12shown in FIG. 5 (b), the detecting planes may be inclined relative tothe bottom of the hollow portions A1 and A2. This allows the detectingplanes to be placed close to the breast and breast peripheries.

(5) In the embodiment described hereinbefore, the detector 11 has ashape of a closed curve with a part thereof cut out, but this is notlimitative. For example, the detector may have a shape forming a cutoutin the shape of a dome having a cavity which can receive a breasttherein. The dome shape may be semispherical, for example. The domeshape may be changed to a conical shape such as of a circular cone orpyramid.

FIG. 8 (a) is a plan view of a detector according to a modifiedembodiment. FIG. 8 (b) is a view in vertical section thereof. In thismodified embodiment, a detector 14 is constructed with a hollow portionA in a shape of a cone (approximately circular cone-shaped).Specifically, detecting planes C of the detector 14 are inclinedrelative to the bottom of the hollow portion A, with an upper part ofthe hollow portion A closed. With the detector 14 constructed in thisway, an entire breast can be accommodated in the hollow portion A, andtherefore the entire breast can easily be put into the field of view.The plate-like member 19 described in Embodiment 1 is dispensable.

(6) In the embodiment described hereinbefore, the hollow portion Aformed in the detector 11 is fixed. A detector may be constructed tohave a hollow portion A variable in size.

FIG. 9 refers. FIG. 9 is a view in horizontal section of a detector 15according to a modified embodiment. The detector 15 is dividable intotwo split detectors 15 a and 15 b. Each of the split detectors 15 a and15 b includes detector blocks 21, and a housing 24 a or 24 b foraccommodating the detector blocks 21.

The split detectors 15 a and 15 b have one ends thereof separated fromeach other, and a cutout B is formed therebetween. At the other ends,the other ends are joined together so that the detecting planes of thesplit detectors 15 a and 15 b may be continuous. And the split detector15 b is pivotably supported by a split pivotal holder 51. The splitpivotal holder 51 is disposed in a position adjacent the other ends ofthe split detectors 15 a and 15 b, and holds the split detector 15 b tobe pivotable while maintaining the continuity of the detecting planes ofthe split detectors 15 a and 15 b. This pivoting operation may bestepless, or a stepped pivoting such as in two steps. Because of spacefor arranging the split pivotal holder 51, even if the detecting planesof the split detectors 15 a and 15 b are not strictly continuous, thedetecting planes may only be close to one another not to affectdiagnosis. Even if the other ends of the split detectors 15 a and 15 b,strictly, are not in contact, but a slight gap is formed therebetween,this is included in the joined state as long as the detecting planes aresubstantially continuous at the other ends.

And with a pivotal movement of the split detector 15 b caused by amanual operation of the operator, the hollow portion A can be enlargedor reduced in size according to the size, shape and so on of a breast.

In the above modified embodiment, the split detector 15 a is fixedlyinstalled. However, the split detector 15 a may also be pivotably heldby the split pivotal holder 51.

(7) In the embodiment described hereinbefore, the rotary support 17supports the detector 11 to be rotatable about one axis P coincidingwith the central axis of the hollow portion A. This is not limitative.As one axis P, an axis parallel to the central axis of the hollowportion A can be selected separately. As one axis P, even an axis notparallel to the central axis of the hollow portion A can be selected asappropriate.

(8) In the embodiment described hereinbefore, the breast peripheries tobe included in the field of view of the detector 11 are exemplified bythe armpit or/and shoulder joint, but these are not limitative. That is,any sites around a breast where breast tissues are present may beselected or varied as appropriate.

(9) The rotary support 17 and the split pivotal holder 51 describedhereinbefore are both manually operable. Instead, a drive device may beprovided separately.

(10) In the embodiment described hereinbefore, the armrest member 18 isin the form of a curved plate. Without being limited to this, a changemay be made to an appropriate shape such as a shape of a flat plate. Thearmrest member 18 closes the cutout B, but instead can be modified notto close it. That is, the mounting position and shape of the armrestmember 18 can be changed as appropriate as long as it can prevent anexcessive entry of an arm and a shoulder. As a result, a gap may beformed. The armrest member 18 is for receiving an arm and a shoulder,and is not limited to receiving of only an arm.

(11) In the embodiment described hereinbefore, the detector 11 has thedetector blocks 21 stacked in two stages, but this is not limitative.For example, the detector blocks 21 may be in one stage, or three ormore stages. The detector 11 is a multilayer ring with scintillatorchips 32 arranged in multiple layers. Without being limited to this, achange may be made to have the scintillator chips 32 arranged in onelayer only.

(12) In the embodiment described hereinbefore, the detector 11 is nottwisted in the direction of the central axis P of the hollow portion A(that is, the detector 11 from one end to the other end thereof is notdisplaced relative to the central axis P). This is not limitative. FIG.10 refers. FIG. 10 is a perspective view of a detector according to amodified embodiment. As shown, a detector 16 may be displaced relativeto an axis Q of the hollow portion A. In other words, a change may bemade to the detector 16 having a shape twisted in the direction of axisQ of the hollow portion A.

(13) Although the embodiment described hereinbefore provides thedetector 11 having the circular hollow portion A, this is notlimitative. The shape of the detector may be designed as appropriatebased on the body surface or shape of an actual or statistically givenpatient (human body) M. Specifically, a change may be made to a detectorhaving a shape extending downward from an armpit to a lower part of abreast, turning back along the lower part of the breast, and extendingto a shoulder joint above the breast. At this time, it is preferred thatthe detector is shaped to be placeable along the body surface.

(14) A detector unit for mammography or a nuclear medicine diagnosticapparatus for mammography may be constructed by combining theconstructions described in the foregoing embodiment and modifications.

1. A detector unit for mammography comprising a gamma-ray detectorhaving a configuration with a cutout formed in part of a closed curve ora polygon having a hollow portion, the hollow portion providing a fieldof view.
 2. A detector unit for mammography comprising a gamma-raydetector having a configuration with a cutout formed in part of a ringshape having a hollow portion, the hollow portion providing a field ofview.
 3. The detector unit for mammography according to claim 1, whereinthe hollow portion is capable of receiving a breast.
 4. The detectorunit for mammography according to claim 1, wherein the gamma-raydetector can be positioned so that, when a top of an arm or a shoulderis inserted in the cutout, at least one of an armpit and a shoulderjoint, and the breast, enter the field of view of the gamma-raydetector.
 5. The detector unit for mammography according to claim 1,wherein the gamma-ray detector has a horseshoe shape or a shape ofletter U.
 6. The detector unit for mammography according to claim 1,wherein the hollow portion is substantially circular.
 7. The detectorunit for mammography according to claim 6, wherein the hollow portion is160 mm to 250 mm in diameter.
 8. The detector unit for mammographyaccording to claim 1, wherein the cutout is 50 to 150 mm in length. 9.The detector unit for mammography according to claim 1, wherein thegamma-ray detector has detecting planes vertical to a bottom plane ofthe hollow portion.
 10. The detector unit for mammography according toclaim 1, wherein the gamma-ray detector has detecting planes inclinedrelative to a bottom plane of the hollow portion.
 11. The detector unitfor mammography according to claim 1, comprising a plate-like object forclosing an outside of a field of view at one side of the hollow portion.12. The detector unit for mammography according to claim 1, comprisingan armrest member in form of a flat plate or a curved plate for closingthe cutout.
 13. The detector unit for mammography according to claim 1,comprising a restricting member disposed in the end regions of thegamma-ray detector for contacting at least one of the top of the arm andthe shoulder to restrict entry of the arm and the shoulder to the hollowportion.
 14. A detector unit for mammography comprising a gamma-raydetector having a configuration with a cutout formed in a dome shape orconical shape having a cavity, the cavity providing a field of view. 15.The detector unit for mammography according to claim 14, wherein thecavity is capable of receiving a breast.
 16. The detector unit formammography according to claim 14, wherein, when a top of an arm or ashoulder is inserted in the cutout, at least one of an armpit and ashoulder joint, and the breast, can be positioned to enter the field ofview of the gamma-ray detector.
 17. The detector unit for mammographyaccording to claim 1, comprising a rotary support device for rotatablysupporting the gamma-ray detector.
 18. The detector unit for mammographyaccording to claim 17, wherein the rotary support device supports thegamma-ray detector to be rotatable about an axis of the hollow portion.19. A nuclear medicine diagnostic apparatus for mammography comprising:a detector unit for mammography according to claim 1; and an imageprocessing device for obtaining an RI distribution image based onemission data collected from the detector unit for mammography.
 20. Thedetector unit for mammography according to claim 2, wherein the hollowportion is capable of receiving a breast.
 21. The detector unit formammography according to claim 2, wherein the gamma-ray detector can bepositioned so that, when a top of an arm or a shoulder is inserted inthe cutout, at least one of an armpit and a shoulder joint, and thebreast, enter the field of view of the gamma-ray detector.
 22. Thedetector unit for mammography according to claim 2, wherein thegamma-ray detector has a horseshoe shape or a shape of letter U.
 23. Thedetector unit for mammography according to claim 2, wherein the hollowportion is substantially circular.
 24. The detector unit for mammographyaccording to claim 23, wherein the hollow portion is 160 mm to 250 mm indiameter.
 25. The detector unit for mammography according to claim 2,wherein the cutout is 50 to 150 mm in length.
 26. The detector unit formammography according to claim 2, wherein the gamma-ray detector hasdetecting planes vertical to a bottom plane of the hollow portion. 27.The detector unit for mammography according to claim 2, wherein thegamma-ray detector has detecting planes inclined relative to a bottomplane of the hollow portion.
 28. The detector unit for mammographyaccording to claim 2, comprising a plate-like object for closing anoutside of a field of view at one side of the hollow portion.
 29. Thedetector unit for mammography according to claim 2, comprising anarmrest member in form of a flat plate or a curved plate for closing thecutout.
 30. The detector unit for mammography according to claim 2,comprising a restricting member disposed in the end regions of thegamma-ray detector for contacting at least one of the top of the arm andthe shoulder to restrict entry of the arm and the shoulder to the hollowportion.
 31. The detector unit for mammography according to claim 2,comprising a rotary support device for rotatably supporting thegamma-ray detector.
 32. The detector unit for mammography according toclaim 31, wherein the rotary support device supports the gamma-raydetector to be rotatable about an axis of the hollow portion.
 33. Anuclear medicine diagnostic apparatus for mammography comprising: adetector unit for mammography according to claim 2; and an imageprocessing device for obtaining an RI distribution image based onemission data collected from the detector unit for mammography.
 34. Thedetector unit for mammography according to claim 14, comprising a rotarysupport device for rotatably supporting the gamma-ray detector.
 35. Thedetector unit for mammography according to claim 34, wherein the rotarysupport device supports the gamma-ray detector to be rotatable about anaxis of the hollow portion.
 36. A nuclear medicine diagnostic apparatusfor mammography comprising: a detector unit for mammography according to14; and an image processing device for obtaining an RI distributionimage based on emission data collected from the detector unit formammography.